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Norman R Harris, Randa S Eshaq; Loss of the Retinal Microvascular Glycocalyx in the Diabetic Rat Retina Occurs with an Increase in Circulating Levels of Matrix Metalloproteinases. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5841.
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© ARVO (1962-2015); The Authors (2016-present)
The aim of this study was to evaluate the hypothesis that the diabetes-induced loss of the retinal microvascular glycocalyx would be associated with increased circulating levels of matrix metalloproteinases (MMPs) in a rat model of type 1 diabetes.
Diabetes was induced in rats via injection of streptozotocin, with age-matched non-diabetic control rats used as controls. Plasma and retinal tissue samples were obtained from the rats eight weeks later, at which time the rats were euthanized. Plasma samples were processed for MMP protein levels (Western blots) and activity (zymography - i.e., degradation of gelatin). The retinas were flatmounted for confocal microscopic imaging of the glycocalyx, where the glycocalyx was stained by Griffonia Simplicifiolia Lectin-1, and with the cleavage of associated glycosaminoglycans (GAGs; specifically heparan sulfate) probed by anti-heparan sulfate delta antibody, which binds to the 3G10 neo-epitope of heparan sulfate that is exposed upon damage or digestion of the GAG.
Staining of the glycocalyx revealed an approximate 95% loss of the capillary glycocalyx in STZ rats compared to controls (p<0.001), with the vasculature in the STZ rat retina demonstrating significant cleavage of heparin sulfate GAGs. Plasma samples revealed a moderate increase in MMP-2 protein levels (p<0.05) and a dramatic increase in MMP-7 activity (p<0.01).
In summary, increases in MMP activity accompany the loss of the retinal glycocalyx in diabetic rats. Further experiments should help clarify the potential cause-and-effect relationship between these events.
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